Method For Depositing Anti-Corrosive Coating Onto Metal Surface

ABSTRACT

The invention provides a method for depositing a stable anti-corrosive metal oxide and/or metal hydroxide layer onto a metal surface. The invention further provides a stable anti-corrosive coating layer on a metal object, which layer comprises metal oxide and/or metal hydroxide.

FIELD OF THE INVENTION

The invention provides a method for depositing a stable anti-corrosive metal oxide and/or metal hydroxide layer onto a metal surface. The invention further provides a stable anti-corrosive coating layer on a metal object, which layer comprises metal oxide and/or metal hydroxide.

BACKGROUND OF THE INVENTION

Every year about 5% of iron products worldwide are being replaced due to corrosion. Various coating methods are used to reduce the corrosion damage, most of which methods are based on applying paints. The corrosion protective element in paints is generally an anti-corrosive pigment (a corrosion inhibitor) based on chromates. These pigments usually include heavy metals salts, which hinder the corrosion of the metal surface. Zinc compounds such as zinc phosphate and zinc chromate are currently widely used as anti-corrosive pigments. Zinc is a heavy metal element and is considered to be toxic at certain concentrations. Due to the growing awareness of the environmental damage associated with heavy metal products, there is an industrial need for effective anti-corrosive coating methods based on non heavy metals, non-toxic agents.

SUMMARY OF THE INVENTION

In one embodiment, this invention provides a method for depositing a stable anti-corrosive metal oxide and/or metal hydroxide layer onto a metal surface including the step of contacting the metal surface with a mixture including, inter alia, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide, thereby depositing the metal oxide and/or the metal hydroxide layer onto the metal surface.

In another embodiment, this invention provides a method for depositing a stable anti-corrosive metal oxide and/or metal hydroxide layer onto a metal surface including the step of contacting the metal surface with a mixture including, inter alia, an organic amine, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide, thereby depositing the metal oxide and/or the metal hydroxide layer onto the metal surface.

Furthermore, in another embodiment, this invention provides a stable anti-corrosive coating layer on a metal object, which layer comprises metal oxide and/or metal hydroxide whereby the layer is obtained by contacting the surface of the object with a mixture including, inter alia, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide.

In another embodiment, this invention provides a stable anti-corrosive coating layer on a metal object, which layer comprises metal oxide and/or metal hydroxide whereby the layer is obtained by contacting the surface of the object with a mixture including, inter alia, an organic amine, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of a Fe reference sample, according to embodiments of the invention;

FIG. 2 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of a Fe sample after 14 days in NaCl 5%, according to embodiments of the invention;

FIG. 3 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of a Fe sample after 14 days in NaCl 5%+ZnP 3%, according to embodiments of the invention;

FIG. 4 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of a Fe sample after 14 days in NaCl 5%+ZnCr 3%, according to embodiments of the invention;

FIG. 5 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of a Fe sample after 14 days in NaCl 5%+E 3%, according to embodiments of the invention;

FIG. 6 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of a Fe sample after 14 days in NaCl 5%+M 3%, according to embodiments of the invention;

FIG. 7 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of an aluminum reference sample, according to embodiments of the invention;

FIG. 8 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of an aluminum sample after 14 days in NaCl 5%+ZnP 3%, according to embodiments of the invention;

FIG. 9 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of an aluminum sample after 14 days in NaCl 5%+ZnCr 3%, according to embodiments of the invention;

FIG. 10 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of an aluminum sample after 14 days in NaCl 5%+E 3%, according to embodiments of the invention;

FIG. 11 shows an Auger spectrum (left); a depth profile chart (middle); and an element concentration table (right) of an aluminum sample after 14 days in NaCl 5%+M 3%, according to embodiments of the invention;

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment, this invention provides a method for depositing a stable anti-corrosive metal oxide and/or metal hydroxide layer onto a metal surface including the step of contacting the metal surface with a mixture including, inter alia, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide, thereby depositing the metal oxide and/or the metal hydroxide layer onto the metal surface.

In another embodiment, this invention provides a method for depositing a stable anti-corrosive metal oxide and/or metal hydroxide layer onto a metal surface including the step of contacting the metal surface with a mixture including, inter alia, an organic amine, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide, thereby depositing the metal oxide and/or the metal hydroxide layer onto the metal surface.

Furthermore, in another embodiment, this invention provides a stable anti-corrosive coating layer on a metal object, which layer comprises metal oxide and/or metal hydroxide whereby the layer is obtained by contacting the surface of the object with a mixture including, inter alia, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide.

In another embodiment, this invention provides a stable anti-corrosive coating layer on a metal object, which layer comprises metal oxide and/or metal hydroxide whereby the layer is obtained by contacting the surface of the object with a mixture including, inter alia, an organic amine, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide.

In one embodiment of the invention, the organic amine and the phosphoric acid and/or inorganic phosphate may react to form an organic phosphate.

In one embodiment of the invention, the organic phosphate may react with the metal oxide and/or metal hydroxide to form oxiaminophosphate. In another embodiment, the oxiaminophosphate is an oxiaminophosphate of a metal. In another embodiment, the metal magnesium.

In one embodiment of the invention, the mixture may include, inter alia, 1-5% of oxiaminophosphate. In another embodiment, the mixture may include, inter alia, 1-3% of oxiaminophosphate. In another embodiment, the mixture may include, inter alia, 3-5% of oxiaminophosphate. In another embodiment, the mixture may include, inter alia, 3% of oxiaminophosphate.

In another embodiment of the invention, the oxiaminophosphate is obtained by adding phosphoric acid and/or inorganic phosphate (4-20%) to water (60-80%) containing an organic amine (2-10%) and then adding metal oxide and/or metal hydroxide (6-25%). In another embodiment, 4-10% of phosphoric acid and/or inorganic phosphate are added to water. In another embodiment, 5-15% of phosphoric acid and/or inorganic phosphate are added to water. In another embodiment, the water contains 2-5% of organic amine. In another embodiment, the water contains 3-7% of organic amine. In another embodiment, 6-10% of metal oxide and/or metal hydroxide are added to the water. In another embodiment, 10-15% of metal oxide and/or metal hydroxide are added to the water. In another embodiment, 15-25% of metal oxide and/or metal hydroxide are added to the water.

In one embodiment of the invention, the organic amine may be, inter alia, a quaternary amine. In another embodiment, the organic amine may be, inter alia, morpholine, dicyclohexylamine, ethanolamine, an aliphatic amine, an aromatic amine, melamine, hexamethylentetramine, pentamethylentetramine or any combination thereof. In another embodiment, the ethanolamine may be mono, di or tri ethanolamine, or any combination thereof.

In one embodiment of the invention, the compound selected from the group consisting of a metal oxide and a metal hydroxide may be formed in solution by adding a base to a metal salt solution.

In one embodiment of the invention, the metal of the metal oxide and/or metal hydroxide may be, inter alia, magnesium, calcium, iron, zinc, molybdenum, aluminum or any combination thereof. In another embodiment, the metal may be, inter alia, magnesium. In another embodiment, the metal oxide may be, inter alia, MgO. In another embodiment, the metal hydroxide may be, inter alia, Mg(OH)₂.

In one embodiment of the invention, the mixture may be, inter alia, a solution, emulsion suspension or slurry. In another embodiment, the mixture may be, inter alia, an aqueous mixture.

In one embodiment of the invention, the thickness of the layer may be between 1-100 nm (nanometer). In another embodiment, the thickness of the layer may be between 5-60 nm. In another embodiment, the thickness of the layer may be between 10-50 nm. In another embodiment, the thickness of the layer may be between 10-20 nm.

In one embodiment of the invention, the mixture may further include, inter alia, surface active agent, anti-corrosive agents, bactericides, colorants, or a combination thereof.

In one embodiment of the invention, the metal surface may include, inter alia, iron, magnesium, aluminum or any combination thereof. In another embodiment, the metal object may include, inter alia, iron, magnesium, aluminum or any combination thereof. In another embodiment, the metal object may be, inter alia, a metal plate or a metal sheet.

EXPERIMENTAL SECTION

Surface analysis was performed using Auger Electron Spectroscopy (AES) on samples of steel and aluminum that were treated with solutions of 5% NaCl.

EXAMPLE 1 Steel Samples

Samples of steel were immersed in solutions of 5% NaCl with or without corrosion inhibitors for a period of two weeks and were then removed and washed with treated water. Surface analysis was performed using Auger electron spectroscopy.

Sample 1: Reference Sample

No NaCl treatment was performed prior to analysis.

Iron oxide, silicon (2.65%), Na (7.56%) and carbon (9.76%), were detected on the surface area. The thickness of the oxide layer was approximately 7 nm (FIG. 1).

Sample 2:

NaCl treatment, no corrosion inhibitors were added to NaCl solution.

Iron oxide, Cl (0.71%), carbon (2.82%), were detected on the surface area. The thickness of the oxide layer was over 50 nm (FIG. 2).

Sample 3:

NaCl treatment, ZnP 3% wt were added to NaCl solution.

Iron oxide, Cl (0.5%) and carbon (10.8%) and Na (5.96%), were detected on the surface area. No phosphorous and zinc were detected on the surface area. Oxygen were detected up to a depth of 90 nm, indicating corrosion (FIG. 3).

Sample 4:

NaCl treatment, ZnCr 3% wt were added to NaCl solution.

Chromium oxide, Zn (38.08%), carbon (3.54%) and Cl (9.86%), were detected on the surface area. The thickness of the chromium and zinc oxide layer was approximately 20 nm (FIG. 4).

Sample 5:

NaCl treatment, E 3% wt were added to NaCl solution.

Unexpected results showed a magnesium oxide layer (Mg conc.=21.26%) having a thickness of approximately 15 nm and low amounts (relative to sample 2) of iron oxide layer having a thickness of approximately 8 nm. In addition, phosphorous (6.71%), carbon (7.57%) and Cl (2.17%), were detected on the surface area (FIG. 5).

“E”, as referred to herein represents an oxyaminophosphate of magnesium which was prepared by adding phosphoric acid (4-20%) to water (60-80%) containing monoethanol amine (2-10%) and then adding MgO (6-25%).

Sample 6:

NaCl treatment, M 3% wt were added to NaCl solution.

Unexpected results showed a magnesium oxide layer (Mg conc.=12.19%) having a thickness of approximately 12 nm and low amounts (relative to sample 2) of iron oxide layer having a thickness of approximately 7 nm. In addition, phosphorous (7.99%), carbon (9.79%), Na (2.30%) and Cl (1.37%), were detected on the surface area (FIG. 6).

“M”, as referred to herein represents an oxyaminophosphate of magnesium which was prepared by adding phosphoric acid (4-20%) to water (60-80%) containing melamine (2-10%) and then adding MgO (6-25%).

EXAMPLE 2 Aluminum Samples

Samples of aluminum were immersed in solutions of 5% NaCl with or without corrosion inhibitors for a period of two weeks and were then removed and washed with treated water. Surface analysis was performed using Auger electron spectroscopy.

Sample 7: Reference Sample

No NaCl treatment was performed prior to analysis.

Aluminum (29.5%), phosphorous (about 2%), carbon (about 14%) and oxygen (about 54%) were detected on the surface area. The depth profile shows a layer of aluminum oxide and/or hydroxide on the surface area having a thickness of approximately 8 nm having a distinctive border with the aluminum (FIG. 7).

Sample 8:

NaCl treatment, ZnP 3% wt were added to NaCl solution.

Aluminum (about 10%), silicon (about 7%), phosphorous (about 6%), Cl (about 0.7%), oxygen (about 66%) and zinc (about 3%) were detected on the surface area. The depth profile shows a layer of aluminum oxide and/or hydroxide on the surface area having a thickness of over 30 nm having no distinctive border with the aluminum. The results show that corrosion of the aluminum was formed. Zinc was found through a 2 nm depth from the surface area and phosphorous was found through a 6 nm depth from the surface area, showing that the ZnP does not provide a sufficient protection to the surface area. (FIG. 8)

Sample 9:

NaCl treatment, ZnCr 3% wt were added to NaCl solution.

Aluminum (about 6.5%), phosphorous (about 4%), carbon (about 13%), Cl (about 2%), oxygen (about 56%), chromium (about 13%), and zinc (about 4%) were detected on the surface area. The depth profile shows a layer of aluminum oxide and/or hydroxide on the surface area having a thickness of approximately 12 nm having a distinctive border with the aluminum. Zinc was found through a 2 nm depth from the surface area and phosphorous was found through a 5 nm depth from the surface area. Even though 13% of chromium is present on the surface area, its concentration at a depth of 2 nm is about 1%. The results show that a 2 nm layer of chromate was formed (FIG. 9)

Sample 10:

NaCl treatment, E 3% wt were added to NaCl solution.

Aluminum (about 0.7%), phosphorous (about 10%), carbon (about 2%), Cl (about 0.3%), oxygen (about 49%) and magnesium (about 38%) were detected on the surface area. The depth profile and the surface analysis show that two layers were formed: one layer comprising oxidized aluminum, oxidized magnesium and phosphorous, the thickness of which layer is approximately 15 nm; and a second layer comprised of aluminum oxide of about 15 micron depth from the surface area (FIG. 10).

Sample 11:

NaCl treatment, M 3% wt were added to NaCl solution.

Aluminum (about 24%), phosphorous (about 14%), carbon (about 10%), Cl (about 0.4%), oxygen (about 45%) and magnesium (about 5%) were detected on the surface area. The depth profile that a layer of aluminum oxide, which comprises also magnesium and phosphorous is formed on the surface area. Phosphorous was found through a 5 nm depth from the surface area. The overall thickness of the oxide layer is approximately 15 nm (FIG. 11).

It will be appreciated that the present invention is not limited by what has been described hereinabove and that numerous modifications, all of which fall within the scope of the present invention, exist. Rather the scope of the invention is defined by the claims that follow: 

1. A method for depositing a stable anti-corrosive metal oxide and/or metal hydroxide layer onto a metal surface comprising the step of: contacting said metal surface with a mixture comprising: an organic amine; a phosphoric acid and/or an inorganic phosphate; and a metal oxide and/or a metal hydroxide, thereby depositing said metal oxide and/or said metal hydroxide layer onto said metal surface.
 2. The method according to claim 1, wherein said organic amine and said phosphoric acid and/or said inorganic phosphate react to form an organic phosphate.
 3. The method according to claim 2, wherein said organic phosphate reacts with said metal oxide and/or said metal hydroxide to form oxiaminophosphate.
 4. The method according to claim 1, wherein said organic amine is a quaternary amine.
 5. The method according to claim 1, wherein said organic amine is morpholine, dicyclohexylamine, ethanolamine, an aliphatic amine, an aromatic amine, melamine, hexamethylentetramine, pentamethylentetramine or any combination thereof.
 6. The method according to claim 5, wherein said ethanolamine is a mono, di or tri ethanolamine or any combination thereof.
 7. The method according to claim 1, wherein said metal oxide and/or said metal hydroxide is formed in solution by adding a base to a metal salt solution.
 8. The method according to claim 1, wherein said metal of said metal oxide and/or said metal hydroxide is magnesium, calcium, iron, zinc, molybdenum, aluminum or any combination thereof.
 9. The method according to claim 8, wherein said metal is magnesium.
 10. The method according to claim 1, wherein said metal oxide is MgO.
 11. The method according to claim 1, wherein said metal hydroxide is Mg(OH)₂.
 12. The method according to claim 1, wherein said mixture is a solution, emulsion suspension or slurry.
 13. The method according to claim 12, wherein said mixture is an aqueous mixture.
 14. The method according to claim 1, wherein the thickness of said layer is between 1-100 nm.
 15. The method according to claim 1, wherein the thickness of said layer is between 5-60 nm.
 16. The method according to claim 1, wherein said metal surface comprises iron, magnesium, aluminum or any combination thereof.
 17. The method according to claim 1, wherein said mixture further comprising surface active agent, anti-corrosive agents, bactericides, colorants, or a combination thereof.
 18. A stable anti-corrosive coating layer on a metal object, which layer comprises metal oxide and/or metal hydroxide whereby said layer is obtained by contacting the surface of said object with a mixture comprising: an organic amine; a phosphoric acid and/or an inorganic phosphate; and a metal oxide and/or a metal hydroxide.
 19. The coating according to claim 18, wherein said organic amine and said phosphoric acid and/or said inorganic phosphate react to form an organic phosphate.
 20. The coating according to claim 19, wherein said organic phosphate reacts with said metal oxide and/or said metal hydroxide to form oxiaminophosphate.
 21. The coating according to claim 18, wherein said organic amine is a quaternary amine.
 22. The coating according to claim 18, wherein said organic amine is morpholine, dicyclohexylamine, ethanolamine, an aliphatic amine, an aromatic amine, melamine, hexamethylentetramine, pentamethylentetramine or any combination thereof.
 23. The method according to claim 22, wherein said ethanolamine is a mono, di or tri ethanolamine or any combination thereof.
 24. The coating according to claim 18, wherein said metal oxide and/or said metal hydroxide is formed in solution by adding a base to a metal salt solution.
 25. The coating according to claim 18, wherein said metal of said metal oxide and/or said metal hydroxide is magnesium, calcium, iron, zinc, molybdenum, aluminum or any combination thereof.
 26. The coating according to claim 25, wherein said metal is magnesium.
 27. The coating according to claim 18, wherein said metal oxide is MgO.
 28. The coating according to claim 18, wherein said metal hydroxide is Mg(OH)₂.
 29. The coating according to claim 18, wherein said mixture is a solution, emulsion suspension or slurry.
 30. The coating according to claim 29, wherein said mixture is an aqueous mixture.
 31. The coating according to claim 18, wherein the thickness of said layer is between 1-100 nm.
 32. The coating according to claim 18, wherein the thickness of said layer is between 5-60 nm.
 33. The coating according to claim 18, wherein said metal object comprises iron, magnesium, aluminum or any combination thereof.
 34. The coating according to claim 18, wherein said mixture further comprising surface active agent, anti-corrosive agents, bactericides, colorants, or a combination thereof.
 35. The coating according to claim 18, wherein said metal object is a metal plate or a metal sheet. 